The interplanetary medium and its interaction with the Earth's magnetosphere

This paper reviews the principal results of direct measurements of the plasma and magnetic field by spacecraft close to the Earth (within the heliocentric distance range 0.7–1.5 AU). The paper gives an interpretation of the results for periods of decrease, minimum and increase of the solar activity. The following problems are discussed: the interplanetary plasma (chemical composition, density, solar wind flow speed, temperature, temporal and spatial variation of these parameters), the interplanetary magnetic field (intensity, direction, fluctuations and its origin), some derived parameters characterizing the physical condition of the interplanetary medium; the quasi-stationary sector structure and its connection with solar and terrestrial phenomena; the magnetohydrodynamic discontinuities in the interplanetary medium (tangential discontinuities and collisionless shock waves); the solar magnetoplasma interaction with the geomagnetic field (the collisionless bow shock wave, the magnetosheath, the magnetopause, the Earth's magnetic tail, the internal magnetosphere characteristics), the connection between the geomagnetic activity and the interplanetary medium and magnetosphere parameters; peculiarities in behaviour of the interplanetary medium and magnetosphere during geomagnetic storms; energetic aspects of the geomagnetic storms.     

Coronal disturbances and their terrestrial effects

Coronal disturbances lead to geomagnetic storms, proton showers, auroras and a wide variety of other phenomena at Earth. Yet, attempts to link interplanetary and terrestrial phenomena to specific varieties of coronal disturbances have achieved only limited success. Here, several recent approaches to prediction of interplanetary consequences of coronal disturbances are reviewed. The relationships of shocks and energetic particles to coronal transients, of proton events to γ-ray bursts, of proton events to microwave bursts, of geomagnetic storms to filament eruptions and of solar wind speed increases to the flare site magnetic field direction are explored. A new phenomenon, transient coronal holes, is discussed. These voids in the corona appear astride the long decay enhancements (LDE's) of 2–50 Å X-ray emission that follow Hα filament eruptions. The transient holes are similar to long-lived coronal holes, which are the sources of high speed solar wind streams. There is some evidence that transient coronal holes are associated with transient solar wind speed increases.     

Global solar magnetic field evolution inferred from geomagnetic variations

I have analyzed geomagnetic disturbance index C9, mean solar magnetic field observed at Stanford Solar Observatory for the interval January 13, 1976 – December 30, 1993. It has been established a good correspondence between high-intensity geomagnetic recurrent and solar magnetic field patterns during whole period analyzed. A surprising thing is that the behavior of the solar mean field and interplanetary medium in the latest two solar cycles is very similar. Geomagnetic activity variations actually could serve as an ecliptic monitor of solar magnetic field structure and its evolution.     

Magnetic field measurements in space

Conclusions The magnetosphere boundary has been penetrated in several places, conflicting evidence about the ring current location has been found, and the field exterior to the boundary has revealed some unexpected features. Pronouncements about the structure of the geomagnetic and interplanetary magnetic fields are still based on scanty evidence but the experimental basis of such estimates is more adequate than in 1958.The boundary between the geomagnetic field and the interplanetary medium has been found, by Explorer XII, to be located at approximately 10 R _E on the sunlit side of the earth near the equator. It has been observed to fluctuate between 8 and 12 R _E during August, September and October of 1961. During several days in March, 1961, the boundary, on the dark side of the earth, was penetrated repeatedly by Explorer X on an outbound pass near 135° from the earth-sun line. Several interpretations are possible; the most reasonable one at present is that the boundary was fluctuating in this period, placing the satellite alternately inside the geomagnetic field and outside in a region of turbulent magnetic fields and plasma flow.A region of turbulent magnetic fields was also observed by Pioneer I, Pioneer V, and Explorer XII between 10 and 15 R _E on the sunlit side of the earth. Pioneer V observed also a steady field 2 to 5 gammas in magnitude beyond 20 R _E. It appears that there exists a region of turbulent magnetic fields between the geomagnetic field boundary near 10 R _E, and another boundary, located near 14–15 R _E near the earth-sun line. This second boundary was seen only by Pioneer I and Pioneer V; Explorer XII and Explorer X apparently did not reach it. This boundary has been tentatively identified as a shock front in the flow of solar plasma about the magnetosphere (see Figure 5).^{41, 42} The geomagnetic field inside the boundary is relatively quiet. An abrupt transition in the magnitude of fluctuations occurs at the boundary surface. The ratio of fluctuation amplitude, B, to average field, B, decreases from 1 to 0.1 on a passage through the boundary on 13 September 1961.⁴³ The boundary is not unstable in the solar wind but fluctuations in solar wind pressure do cause changes in boundary location.^42,43 The ring current location appears to be above 1.4 R _E and below 5 R _E on the basis of Pioneer I, Vanguard III, and Explorer XII data. Lunik I and II records indicate that it is located between 3 and 4 R _E. Explorer VI data indicates that it must be at distances greater than 4 R _E on the dark side of the earth. Some variation in altitude of a ring current with time appears likely, but the bulk of present evidence limits a possible ring current to a distance of 3 to 5 R _E.The interplanetary field during quiet times is of the order of 2 to 5 gammas. The direction indicated for this field, with a significant component perpendicular to the earth-sun line, is puzzling in view of solar cosmic ray transit times. Solar disturbances with resultant plasma flow past the satellite produce increases in the field magnitude. Field increases at the satellite are sometimes correlated with disturbances observed at the earth.Further investigations are needed to map the magnetosphere and boundary more completely, to investigate the postulated shock front and the turbulent region inside, to refute or confirm the ring current theory, and to measure the interplanetary field direction and magnitude more completely. Theoretical studies are needed to support these experiments and to suggest new avenues of investigations. Particularly needed are theoretical investigations of collisionless shock fronts in plasma flow and of characteristics of the flow between the shock front and the obstacle.     

Discontinuities in the solar wind

The nonuniform emission of the solar wind from the sun means that conditions are established which favor the development of discontinuities in the plasma parameters. Since the solar wind is in rapid proper motion with respect to the sun and the earth, examination of these discontinuities requires that the wind velocity be transformed away. Then it is found that they satisfy the conditions of magnetohydrodynamics and can be treated as shock waves and the stationary contact surfaces consisting of either tangential or contact discontinuities. The collision-free structure of the solar wind suggests that the tangential discontinuity is the more likely contact surface as it is more capable of inhibiting diffusion which is required for a lifetime sufficient for the structure to be carried to the neighborhood of the earth.Either the shock wave or the contact surface can create signals that are detectable at the surface of the earth. The simplest surface signal to detect is the sudden impulse (SI) but other signals may be found. The existence of a field of MHD discontinuities in the solar wind should make possible the generation of ensembles of shocks and contact surfaces. Various possibilities are explored and these are discussed from the standpoint of combinations of sudden impulses at the earth's surface which are both positive and negative. Some of these are recurrent with a 27-day period; the interplanetary M region shock ensemble associated with this is discussed and the development of these structures in space is reviewed.Lastly observational evidence for interplanetary shock waves is given together with the analytic technique for establishing their geometry and comparing the derived and measured jump parameters. The applicability of the geometrical construction of the general class of MHD discontinuity to their analysis is indicated and shows the way in which the structural content of the solar wind can be classified by the use of magnetometers and plasma probes. A parametric study of the jump conditions through a shock wave can be used to verify the correctness of field measurements because of the redundancy in measurements. This also allows the details of shock structure to be examined including the intrinsic partitioning of the internal energy of the shocked plasma.     

Fields and plasmas in the outer solar system

The most significant information about fields and plasmas in the outer solar system, based on observations by Pioneer 10 and 11 investigations, is reviewed. The characteristic evolution of solar wind streams beyond 1 AU has been observed. The region within which the velocity increases continuously near 1 AU is replaced at larger distances by a thick interaction region with abrupt jumps in the solar wind speed at the leading and trailing edges. These abrupt increases, accompanied by corresponding jumps in the field magnitude and in the solar wind density and temperature, consist typically of a forward and a reverse shock. The existence of two distinct corotating regions, separated by sharp boundaries, is a characteristic feature of the interplanetary medium in the outer solar system. Within the interaction regions, compression effects are dominant and the field strength, plasma density, plasma temperature and the level of fluctuations are enhanced. Within the intervening quiet regions, rarefaction effects dominate and the field magnitude, solar wind density and fluctuation level are very low. These changes in the structure of interplanetary space have significant consequences for the many energetic particles propagating through the medium. The interaction regions control the access to the inner solar system of relativistic electrons from Jupiter's magnetosphere. The interaction regions and shocks appear to be associated with an acceleration of solar protons to MeV energies. Flare-generated shocks are observed to be propagating through the outer solar system with constant speed, implying that the previously recognized deceleration of flare shocks takes place principally near the Sun. Radial gradients in the solar wind and interplanetary field parameters have been determined. The solar wind speed is nearly constant between 1 and 5 AU with only a slight deceleration of 30 km s⁺¹ on the average. The proton flux follows an r ⁺² dependence reasonably well, however, the proton density shows a larger departure from this dependence. The proton temperature decreases steadily from 1 to 5 AU and the solar wind protons are slightly hotter than anticipated for an adiabatic expansion. The radial component of the interplanetary field falls off like r ⁺² and, on the average, the magnitude and spiral angle also agree reasonably well with theory. However, there is evidence, principally within quiet regions, of a significant departure of the azimuthal field component and the field magnitude from simple theoretical models. Pioneer 11 has obtained information up to heliographic latitudes of 16°. Observations of the interplanetary sector structure show that the polarity of the field becomes gradually more positive, corresponding to outward-directed fields at the Sun, and at the highest latitudes the sector structure disappears. These results confirm a prior suspicion that magnetic sectors are associated with an interplanetary current sheet surrounding the Sun which is inclined slightly to the solar equator.Proceedings of the Symposium on Solar Terrestrial Physics held in Innsbruck, May–June 1978.     

Theoretical studies of the solar wind phenomenon

This paper is a review of current theoretical topics concerning the solar wind. Broadly speaking the questions outstanding at the present time concern the loss of angular momentum to the sun, the origin of the fluctuations observed in the wind at the orbit of earth, conditions in the wind in regions yet unvisited by spacecraft (inside the orbit of Venus, beyond the orbit of Mars, and out of the plane of the ecliptic), conditions at the terminus of the wind, etc. The question of angular momentum loss is important in understanding the evolution of the sun to its present form with a slowly rotating surface. Evidence from both comet and spacecraft observations of the wind indicate that the rate at which angular momentum is being carried away by the solar wind is very large, of the order of 10³¹ dyne/cm in the gas flow and half as much by the interplanetary magnetic field. But theory cannot account for more than about 10³⁰ dynes/cm in the gas without special assumptions.The fluctuations presently observed in the wind at the orbit of earth have scales ranging upward from 10² km. Their presence is puzzling because fluctuations with scales less than about 10⁶ km are not expected to survive from the sun. Presumably, therefore, the fluctuations are generated by the velocity differences of more than 100 km/sec in the wind from different regions in the solar corona and by instabilities produced by the anisotropy of the electrons of the wind plasma.Conditions in the wind at places far removed from the orbit of earth can be inferred from the behavior of cosmic rays. The evidence is that the wind becomes relatively placid beyond about 5 AU, extending from there out to 30–300 AU without much small-scale turbulence. There are also some suggestions that the wind may perhaps be less turbulent toward the sun from 1 AU, and that the wind may be faster and more turbulent at higher solar latitudes. But the ambiguity of the situation does not permit a firm conclusion on this yet.     

Latitudinal structure of the solar wind and interplanetary magnetic field

A review is given of both observational and theoretical results concerning the latitudinal structure of the solar wind and interplanetary magnetic field. Observations are reported on the solar wind plasma and magnetic fields, obtained both from direct satellite measurements and indirect methods, such as the observation of comet tails, radio scintillations, the study of the polar geomagnetic field and the semi-annual variation of geomagnetic activity. Results of theoretical work, both on three-dimensional modelling of the solar wind and on gas-magnetic field interactions in the solar corona are summarized. Finally, an attempt is made to compare available observations and theories. This points to the open questions which, to be settled, will need direct observations of plasma and magnetic field at high heliographic latitudes.     

Large-scale electric field in the magnetosphere

A review is given on the distribution and origin of the large-scale electric field in the magnetosphere and its influence on the dynamical behavior of the magnetospheric plasma. Following a general discussion on the gross structure of the magnetosphere and its tail, two principal electric field systems are deduced from ground-based geomagnetic variations. One is responsible for the polar substorm, the DP 1 field, which is closely associated with the activation of the auroral electrojet. The other is responsible for the twin current vortices, the DP 2 field, and this represents the general convective system set up in the magnetospheric plasma.The origin of these magnetospheric electric fields is possibly resided in the domain of the solar wind interacting with the outer geomagnetic field. However, the mechanism, in which the energy is transferred, is still quite controversial. Several theories so far proposed are re-examined, and some modification of them are suggested to have a consistent understanding of these two types of electric fields. The effects of electric fields on magnetospheric plasma dynamics are described, such as the formation of the plasmapause, the acceleration and diffusion of energetic particles in the radiation belt.     

The storm-time ring current

In this paper I am reviewing recent advances and open disputes in the study of the terrestrial ring current, with emphasis on its storm-time dynamics. The ring current is carried by energetic charged particles flowing toroidally around the Earth, and creating a ring of westward electric current, centered at the equatorial plane and extending from geocentric distances of about 2 R _E to roughly 9 R _E. This current has a permanent existence due to the natural properties of charged particles in the geospace environment, yet its intensity is variable. It becomes more intense during global electromagnetic disturbances in the near-Earth space, which are known as space (or magnetic or geomagnetic) storms. Changes in this current are responsible for global decreases in the Earth's surface magnetic field, which is the defining feature of geomagnetic storms. The ring current is a critical element in understanding the onset and development of space weather disturbances in geospace. Ring current physics has long been driven by several paradigms, similarly to other disciplines of space physics: the solar origin paradigm, the substorm-driver paradigm, the large-scale symmetry paradigm, the charge-exchange decay paradigm. The paper addresses these paradigms through older and recent important investigations.     

Solar modulation of galactic cosmic radiation

In this review an attempt is made to present an integrated view of the solar modulation process that cause time variation of cosmic ray particles. After briefly surveying the relevant large and small scale properties of the interplanetary magnetic fields and plasma, the motion of cosmic ray particles in the disordered interplanetary magnetic fields is discussed. The experimentally observed long term variations of different species of cosmic ray particles are summarised and compared with the theoretical predictions from the diffusion-convection model. The effect of the energy losses due to decelaration in the expanding solar wind are clearly brought out. The radial density gradient, the modulation parameter and their long term variation are discussed to understand the dynamics of the modulating region. The cosmic ray anisotropy measurements at different energies are summarised. At high energies (E 1 GeV), the average diurnal anisotropy is shown to be energy independent and along the 18.00 h direction consistent with their undergoing partial corotation with the sun. The average semi-diurnal anisotropy seems to vary with energy as E ⁺¹ and incident from a direction perpendicular to the interplanetary field line, consistent with the semi-diurnal component being produced by latitudinal gradients. Both the diurnal and semi-diurnal components are shown to be practically time invariant. On a day to day basis, however, the anisotropy characteristics such as the exponent of variation, the amplitude and the phase show very high variability which are interpreted in terms of convection and variable field aligned diffusion due to the redistribution of the galactic cosmic ray density following transient changes in the interplanetary medium. The anisotropy observation at low energies (E 100 MeV) are, however, not explained by the theory.The rigidity dependence and the anisotropies during short term variations such as Forbush decreases are discussed in terms of the proposed field models for the interplanetary field structure and are compared with the observed rigidity dependence of long term variations. The data pertaining to the 27 day corotating Forbush decreases and their association with enhanced diurnal variation are also presented. The relationship between the energetic storm particle events which are caused by the acceleration of particles in the shock fronts and the Forbush decreases which are caused by the exclusion of galactic particles by the enhanced field structure in the same fronts are clearly brought out. Thus the recurrent increases at low energies and recurrent decreases at high energies may both be caused by the field structure in the shock front. In conclusion, the properties of the very short period fluctuations (18–25 cph) are summarised.     

Interplanetary streams and their interaction with the earth

Plasma and magnetic field observations of interplanetary streams near 1 AU are summarized. Two types of streams have been identified — corotating streams and flare-associated, and other flow patterns are present due to interactions among streams. The theory of corotating streams, which attributes them to a high temperature region near the Sun, satisfactorily explains many of the effects observed at 1 AU. A correspondingly complete theory of flare-associated streams does not exist. Streams are a key link in the chain that connects solar and geomagnetic activity. The factors that most influence geomagnetic activity are probably related to streams and determined by the dynamics of streams. The evolution of streams on scales of 27 days and 11 years probably determines the corresponding variations of geomagnetic activity.     

Ring Current Dynamics

This chapter reviews the current understanding of ring current dynamics. The terrestrial ring current is an electric current flowing toroidally around the Earth, centered at the equatorial plane and at altitudes of ∼10,000 to 60,000 km. Enhancements in this current are responsible for global decreases in the Earth’s surface magnetic field, which have been used to define geomagnetic storms. Intense geospace magnetic storms have severe effects on technological systems, such as disturbances or even permanent damage of telecommunication and navigation satellites, telecommunication cables, and power grids. The main carriers of the ring current are positive ions, with energies from ∼1 keV to a few hundred keV, which are trapped by the geomagnetic field and undergo an azimuthal drift. The ring current is formed by the injection of ions originating in the solar wind and the terrestrial ionosphere into the inner magnetosphere. The injection process involves electric fields, associated with enhanced magnetospheric convection and/or magnetospheric substorms. The quiescent ring current is carried mainly by protons of predominantly solar wind origin, while active processes in geospace tend to increase the abundance (both absolute and relative) of O⁺ ions, which are of ionospheric origin. During intense geospace magnetic storms, the O⁺ abundance increases dramatically. This increase has been observed to occur concurrently with the rapid intensification of the ring current in the storm main phase and to result in O⁺ dominance around storm maximum. This compositional change can affect several dynamic processes, such as species-and energy-dependent charge-exchange and wave-particle scattering loss.     

Interplanetary studies: Propagation of disturbances between the Sun and the magnetosphere

This review is concerned with the interplanetary ‘transmission line’ between the Sun and the Earth's magnetosphere. It starts with comments about coronal mass ejections (CMEs) that are associated with various forms of solar activities. It then continues with some of the current views about their continuation through the heliosphere to Earth and elsewhere. The evolution of energy, mass, and momentum transfer is of prime interest since the temporal/spatial/magnitude behavior of the interplanetary electric field and transient solar wind dynamic pressure is relevant to the magnetospheric response (the presence or absence of geomagnetic storms and substorms) at Earth. Energetec particle flux predictions are discussed in the context of solar activity (flares, prominence eruptions) at various positions on the solar disk relative to Earth's central meridian. A number of multi-dimensional magnetohydrodynamic (MHD) models, applied to the solar, near-Sun, and interplanetary portions of the ‘transmission line’, are discussed. These model simulations, necessary to advancing our understanding beyond the phenomenological or morphological stages, are directed to deceptively simple questions such as the following: can one-to-one associations be made between specific forms of solar activity and magnetosphere response?     

Large-scale and solar-cycle variations of the solar wind

This paper summarizes space probe observations relevant to the determination of the large-scale, three-dimensional structure of the solar wind and its solar cycle variations. Observations between 0.6 and 5 AU reveal very little change in the average solar-wind velocity, but a pronounced decrease in the spread of velocities about the average. The velocity changes may be accompanied by a transfer of energy from the electrons to the protons. The mass flux falls off approximately as the inverse square of distance as expected for spherically symmetric flow. Measurements of the interplanetary magnetic field show that the spiral angle is well defined over this entire range of distances, but there is some evidence that the spiral may wind up more slowly with distance from the Sun than predicted by Parker's model. The variances or noise in the field and plasma have also been measured as a function of radial distance.During the rising portion of the solar-activity cycle, the solar-wind velocity showed a pronounced positive correlation with solar latitude over the range ±7°. Several other plasma parameters which have been found generally to correlate (or anticorrelate) with velocity also showed a latitude variation; these parameters include the density, percent helium, and azimuthal flow direction. The average polarity and the north-south component of the magnetic field depend on the solar hemisphere in which the measurements are made.Dependence on the phase of the solar-activity cycle can be found in the data on the number of high speed streams, the proton density, the percent helium, and the magnetic-field strength and polarity.     

Polar auroras

Conclusion We have reviewed the somewhat conflicting data which have accumulated on such a vast scale in recent years. It is now becoming clearer which studies are likely to produce significant results, and this in itself may be a very important consequence of the assimilation of accumulated data. We must however ask in conclusion: does the outer radiation belt exist during the polar aurora? If the interplanetary media or the solar wind, carry magnetic fields, then these fields can be of two kinds. Firstly, they may be magnetic lines of force dragged by the plasma from the Sun. Secondly, the interplanetary medium or the solar wind are capable of carrying closed magnetic lines of force which are not related to the Sun. When such fields approach the Earth, the high-latitude geomagnetic lines of force which previously passed through the equatorial plane on the boundary of the magnetosphere, may deform in such a way as to pass out of one geomagnetic poles, miss the equatorial plane, enter the interplanetary plasma, and after passing through a very considerable volume of this plasma reach the other geomagnetic pole. This will in effect amount to an attachment through the medium of magnetic lines of force of enormous regions of ionised interplanetary matter or of solar wind to the Earth's magnetosphere. As these extraneous magnetic fields depart from the Earth's neighbourhood, the original dipole field will be reestablished. Rapid variations in the configuration of the geomagnetic field will occur during the interaction. It is possible that energetic particles appear with a very high degree of probability on the boundary of the geomagnetic field during such deformations. If this is so, then the outer radiation belt is merely a temporary formation appearing during the quiet intervals between geomagnetic disturbances, and containing a small residue of energetic charged particles, which exist during the polar auroras but do not succeed in entering the lower atmosphere during this time. In this process the particles giving rise to the polar auroras originate in the plasma of the solar corpuscular streams flowing past the Earth.Under the action of a solar wind the geomagnetic field is compressed at the front and elongated at the rear. This resembles the original Chapman theory of geomagnetic storms more closely than any other theory. Since the elongated geomagnetic field on the night side of the Earth is of a lower intensity, it may be associated with the magnetic fields brought in by the incident medium right down to very great depths. This may be responsible for the observed displacement at the zone of the polar auroras towards lower geomagnetic latitudes at night.Translated by the Express Translation Servies, Wimbledon, London.     

The streaming of solar flare particles and plasma in interplanetary space

A review is given of the features of solar particle emissions which cause various terrestrial disturbances. Three types of corpuscular emissions, namely, solar cosmic rays, energetic storm protons and plasma clouds, are associated with intense solar flares. Outward streaming of the solar wind and of beams of enhanced activity originate from the quiescent solar corona. It is shown that these solar particles propagate through interplanetary space, being modulated in a systematic way by existing magnetic fields. Time variations of solar flare particle flux, and their energy spectrum, are discussed.     

Simulation of three-dimensional solar wind disturbances and resulting geomagnetic storms

A kinematic method of representing the three-dimensional solar wind flow is devised by taking into account qualitatively the stream-stream interaction which leads to the formation of a shock pair. Solar wind particles move radially away from the Sun, satisfying the frozen-magnetic field condition. The uniqueness of the present approach is that one can incorporate both theoretical and observational results by adjusting the parameters involved and that a self-consistent data set can be simulated. One can then infer the three-dimensional structure of the solar wind which is vital in understanding the interaction between the solar wind and the magnetosphere, and it is for this reason that the present kinematic method is devised. In the first part of this paper, the present kinematic method is described in detail by demonstrating that the following solar wind features can be simulated: (i) Variations of the solar wind quantities (such as the solar wind speed, the density and the IMF vector), associated with the solar rotation, at the Earth; (ii) the solar wind flow pattern in the meridian planes; (iii) the three-dimensional structure of the corotating interaction region (CIR); and (iv) the three-dimensional structure of the warped solar current sheet.In Section 2, the three-dimensional structure of solar wind disturbances are studied by introducing a flare-generated high speed stream into the two-stream model of the solar wind developed in Section 1. The treatment of the stream-stream interaction is generalized to deal with a flare-generated high speed stream, yielding a shock pair. The shock pair causes three-dimensional distortion of the solar current sheet as it propagates outward from the Sun. It is shown that a set of characteristic time variations of the solar wind speed, density, the interplanetary magnetic field magnitude B and angles (theta) and gf (phi) result at the time of the passage at the location of the Earth for a given set of flare conditions. These quantities allow us to compute the solar wind-magnetosphere energy coupling function . Time variations of the two geomagnetic indices AE and Dst are then estimated from . The simulated geomagnetic storms are compared with observed ones.In the third part, it is shown that recurrent geomagnetic storms can reasonably be reproduced, if fluctuating components of the interplanetary magnetic field (IMF) are superposed on the kinematic model of the solar wind developed in the first part. As an example, we simulate the fluctuating components by linearly polarized Alfvén waves and by random variations of the IMF angle (theta). Characteristics of the simulated and observed geomagnetic storms are discussed in terms of the simulated and observed AE and Dst indices. If the fluctuating components of the IMF can generally be identified as hydromagnetic waves, they may be an important cause for individual magnetospheric substorms, while the IMF magnitude B and the solar wind speed V modulate partially the intensity of magnetospheric substorms and storms.     

Solar cosmic rays

The first observations of solar cosmic rays were made simultaneously by many investigators at worldwide cosmic-ray stations in the periods of powerful chromospheric flares on February 28 and March 7, 1942. The discovery of these and the investigation of cosmic-ray solar-daily variations with maximum time near noon led some authors (Richtmyer and Teller, 1948; Alfvén, 1949, 1950) to a model of apparent cosmic-ray solar origin. We present here the results of the properties of solar cosmic rays from ground events (experimental and theoretical investigations). We also discuss important information from solar experimental data relating to these ground events observed in September and October 1989 and May 1990. Some experimental evidence of acceleration processes in associated phenomena with flares and long-term (solar cycle) variation of the average flux of solar cosmic rays is discussed as also cornal and interplanetary propagation, and that in the terrestrial magnetosphere. Note that the energy spectrum of solar cosmic rays varied very strongly from one flare to another. What are the causes of these phenomena? What is the nature of chemical and isotopic contents of solar cosmic rays? How can its changes occur in the energy spectrum and chemical contents of solar cosmic rays in the process of propagation? Is it possible to recalculate these parameters to the source? What makes solar cosmic rays rich in heavy nucleus and³He? The important data about electrons, positrons, gamma-quanta and neutrons from flares will be discussed in a subsequent paper (Dorman and Venkatesan, 1992). The question is: What main acceleration mechanism of solar flare and associated phenomena are reliable? These problems are connected with the more general problem on solar flare origin and its energetics. In Dorman and Venkatesan (1993) we will consider these problems as well as the problem of prediction of radiation hazard from solar cosmic rays (not only in space, but also in the Earth's atmosphere too).